The invention relates to an electronic component with at least one semiconductor chip, and to a method for producing the electronic component.
Electronic semiconductor chips can be connected to rewiring boards or layers and printed circuit boards to make so-called chip size packages (CSPs). The electrical and mechanical connections between the individual components can contain soldered wire connections. The soldered connections, which by now are made with lead-free solder, must be heated to temperatures of at least 240xc2x0 C. This puts a considerable temperature stress on the vulnerable semiconductor components. Once the CSPs have been produced, test routines are performed for functionally testing the semiconductor chips; if the outcome is negative, the already-soldered semiconductor chips have to be replaced. Besides the effort of handling, which involves labor costs and slows down production, this also results in another high temperature stress on the components.
It is accordingly an object of the invention to provide an electronic component with at least one semiconductor chip and a method for producing the electronic component which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, which furnishes a fast component connection, which can be produced economically, between a semiconductor chip, a rewiring layer and a printed circuit board that moreover enables fast replacement of an already-mounted semiconductor chip.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic component. The electronic component contains at least one semiconductor chip, a rewiring layer connected to the semiconductor chip and has a surface remote from the semiconductor chip, a printed circuit board associated with the rewiring layer, and contact faces disposed on the printed circuit board. Flexible contacts are disposed on the surface of the rewiring layer remote from the semiconductor chip. The flexible contacts correspond with the contact faces on the printed circuit board. A flat intermediate layer solidly connects the rewiring layer to the printed circuit board.
According to the invention, the electronic component has the semiconductor chip, the rewiring layer connected to the semiconductor chip, and the printed circuit board associated with the rewiring layer. It is provided that the rewiring layer has flexible contacts, which correspond to contact faces of the printed circuit board, and that the rewiring layer is solidly connected to the printed circuit board via a flat intermediate layer.
The electronic component of the invention has the advantage that a separable component connection between the rewiring layer, with the at least one semiconductor chip mounted on it, and the printed circuit board can be produced quickly and inexpensively. Moreover, the mounting can be done with a very high throughput, without having to make soldered connections that would represent a considerable temperature stress and an unavoidable expenditure of time in processing the components. A single semiconductor chip can be mounted on the rewiring layer. However, electronic components with many semiconductor chips on a single rewiring layer are also possible. It is also possible for one or more rewiring layers to be mounted on one printed circuit board, so that optionally, very large scale integration electronic components can be achieved.
In a first embodiment of the invention, the rewiring layer, having the at least one semiconductor chip, and the printed circuit board are mounted at a defined spacing from one another. This has the advantage that the flexible contacts of the rewiring layer are placed with a defined contact to the contact faces of the printed circuit board and assure a secure electrical contact of the two components. Depending on the size of the flexible contacts, the defined spacing can advantageously be in a range from about 50 xcexcm to 200 xcexcm, making extremely compact structural heights of the chip size packages (CSPs) feasible.
In a further embodiment of the invention, when the rewiring layer has been mounted on the printed circuit board, the flexible contacts are prestressed. This has the advantage of a defined contact force of the flexible contacts, thus assuring a secure electrical contact between the touching faces, which are metal. The elasticity, perpendicular to the component surface, of the flexible contacts moreover assures a certain composition for unevenness and raised areas of the rewiring layer or of the printed circuit board relative to one another.
One embodiment of the invention provides that the flexible contacts protrude slightly past the flat intermediate layer between the rewiring layer and the printed circuit board, in the unstressed state. The embodiment has the advantage of a reliable connection at all times between the flexible contacts and the contact faces of the printed circuit board, since the flexible contacts are initially elastically deformed, until they mechanically impact the flat intermediate layer and thus form a reliable electrical contact.
In another embodiment of the invention, the flat intermediate layer contains a plastic, which has the advantage of simple, economical processabilityxe2x80x94for example by injection molding. Moreover, plastic acts as an electrical and thermal insulator, so that it is advantageously suitable as a touch layer, even of current-carrying regions of the semiconductor chip or of the rewiring layer.
In a further embodiment of the invention, the flat intermediate layer is embodied in multiple parts, and only at interstices between adjacent flexible contacts and/or groups of flexible contacts is it applied. This has the advantage that the flexible contacts have enough clearance for deformation at all times, without striking the intermediate layer in their elastic flexing.
One embodiment of the invention provides that the flat intermediate layer is perforated, and that flexible contacts are disposed in the interstices. This embodiment has the advantage of particular stability, because of the grid-net shaped structure formed as a result. This also makes it possible to simplify processability in a single, fast injection molding process.
In one embodiment of the invention, the flat intermediate layer is a film that is adhesive on both sides, which has the advantage of especially simple, extremely fast processability. The film can be applied in one step, immediately after which the rewiring layer can be pressed onto the printed circuit board. This makes for very fast cycle times and thus a very high throughput in production of the electronic components of the invention.
In a further embodiment of the invention, the flat intermediate layer is embodied as a one-piece perforated or multi-part base on the rewiring layer, over which a thin adhesive film is secured. This base can be applied in a simple way, for instance using a pressing technique, and has a defined thickness. The thin adhesive film applied over it then assures a solid bond between the base, which is already solidly connected to the rewiring layer, and the printed circuit board. The base can advantageously contain a polymer material, for instance, which makes it especially simple to process. As needed, the base can be in multiple parts, with the parts each disposed in interstices between flexible contacts. A one-piece version in a grid-net shaped structure is equally possible.
An alternative embodiment of the invention provides that the flat intermediate layer is embodied as a one-piece perforated or multi-part base on the printed circuit board, over which a thin adhesive film is secured. This has the advantage that compared with the above embodiment, a defective semiconductor chip can be easily removed from the printed circuit board again and replaced with an intact one.
One embodiment of the invention provides that the adhesive bond adheres more strongly to the printed circuit board than to the rewiring layer, which has the advantage of a defined parting point when a defective semiconductor chip is being removed. This prevents the adhesive film from detaching from the base before the rewiring layer is separated from the film.
In a further embodiment of the invention, the adhesive bond is embodied detachably on the rewiring layer, which in particular has the advantage of fast, simple removability of a semiconductor chip that has been tested and found defective.
In a further embodiment of the invention, the adhesive bond on the rewiring layer can be reused repeatedly, after a mounted rewiring layer has been detached, which has the special advantage that a tested semiconductor chip found to be defective can easily be replaced with an intact one. No further application steps whatever, such as applying a new adhesive point or the like, are required for this.
An embodiment of the invention provides that the flexible contacts are embodied in the form of a contact hump. This has the advantage of uniform elastic deformation when the rewiring layers are applied to the printed circuit boards. A curved contour then assures a uniform distribution of the spring force over the entire course of the contact hump.
An embodiment of the invention provides that the flexible contacts are in touch contact with the respective corresponding contact faces of the printed circuit board. This embodiment has the advantage of a simple, very quickly made electrical connection between the semiconductor chip, the rewiring layer and the printed circuit board, without requiring more-extensive processing stepsxe2x80x94such as soldering or the like. Moreover, in such a case, a defective semiconductor chip can especially easily be replaced with a new component, without first having to undo the electrical connection points.
An alternative embodiment of the invention provides that the flexible contacts are soldered and/or glued to the respectively corresponding contact faces of the printed circuit board. This alternative embodiment has the advantage of an especially stable, strong mechanical and electrical connection between the contact points.
In a method of the invention for producing an electronic component with at least one semiconductor chip, a rewiring layer connected to the at least one semiconductor chip, and a printed circuit board associated with the rewiring layer, it is provided that the rewiring layer is provided with flexible contacts, which correspond with contact faces of the printed circuit boards. It is also provided that the rewiring layer is solidly connected to the printed circuit board via a flat intermediate layer. According to the invention, the method is characterized by the now described method steps. After a semiconductor wafer has been produced, with semiconductor chips disposed in rows and columns, with saw-scoring regions provided between them, the chips are each connected to the rewiring layers. On the surface of the rewiring layer remote from the active side of the semiconductor chip, flexible contacts are applied. After that, flat intermediate layers are applied to the rewiring layers, after which the rewiring layers are glued to printed circuit boards. It is selectively possible either for only one, or for a plurality of, semiconductor chips to be applied to one rewiring layer. It is equally possible selectively for only one or for a plurality of rewiring layers to be applied to one printed circuit board.
This production method of the invention has the particular advantage that so-called CSPs can be produced quickly and inexpensively, and moreover, soldering which is a burden to the components can be dispensed with. The adhesive bonding of the rewiring layers to the printed circuit boards assures a solid, stable mechanical connection, while conversely the electrical connection is made by resilient contacts, which are entirely relieved of any mechanical carrier function. The flexible contacts instead slide along contact faces of the printed circuit board and are pressed slightly against them, until the rewiring layer comes to rest on the intermediate layer. Thus integrated electronic components, which are distinguished by a large scale of integration and high mechanical stability, can be produced in extremely short cycle times.
In a first exemplary embodiment of the method of the invention, the semiconductor wafer is cut apart into semiconductor chips, after the flexible contacts have been applied and before the rewiring layers are applied. This has the advantage that flexible production of different electronic components on the same production line is made possible. When the semiconductor chips are cut apart first and only after that are connected to rewiring layers, then optionally different components can be grouped on the same line and joined together.
In an alternative exemplary embodiment of the method, the semiconductor wafers are cut apart into electronic components after the rewiring layers have been mounted on the semiconductor chips. This has the advantage of especially fast processing in relatively large batches. If the rewiring layers are already connected to the semiconductor wafer, many electronic components can be produced in one operation that are only separated into individual components in a subsequent processing step. The rewiring layers can then selectively be sawn apart along with the wafer, or they can already be joined as individual parts to the semiconductor chips that are to be cut apart.
One embodiment of the method of the invention provides that a film that is adhesive on both sides is applied as a flat intermediate layer between the rewiring layer and the printed circuit board, which has the advantage of a very easily manipulated, stable component connection between the rewiring layer and the printed circuit board.
Another embodiment of the method of the invention is characterized in that as the flat intermediate layer, a base is applied to the rewiring layer or to the printed circuit board, and over it a thin adhesive film is applied. This embodiment has the advantage that the stable base can be embodied with very exact dimensional fidelity in a simple way, while conversely, a commercially available film can be used as the thin adhesive film. As the base, a thermoplastic, for instance, or the like can be considered, which can be processed by injection molding.
In an embodiment of the method of the invention, the adhesive bond adheres more strongly to the printed circuit board than to the rewiring layer, which has the advantage that a semiconductor chip tested and found defective can be detached again from the printed circuit board in a simple way, without the risk of separation of the adhesive film.
Finally, one embodiment of the method of the invention provides for adhesive bonding and/or soldering of the flexible contacts to the corresponding contact faces of the printed circuit board. This has the advantage of an even more-stable mechanical connection between the printed circuit board and the rewiring layer. Furthermore, it can be assured even more certainly in this way that all the flexible contacts will carry the electric current, and that a defective connection will not be made, for instance because of a poor contact.
A final exemplary embodiment of the invention provides that the semiconductor chips are tested after the rewiring layer is mounted on the printed circuit board, and that after a defective semiconductor chip is found, the adhesive bond can be undone and reused. This exemplary embodiment has the special advantage of fast, uncomplicated replaceability of defective parts. This replacement can be done in very short cycles; moreover, a new semiconductor chip can be placed without difficulty over the previously released adhesive point, without requiring any further processing steps of any kind.
In summary, the following aspects of the present invention are obtained. The basic concept is the configuration of a so-called chip size package (CSP) with so-called interconnect elements that are elastic in the vertical direction, and in the attachment of such a chip on a board or printed circuit board of a commercially available kind, at a suitable prestressing of the elastic interconnect elements, thus creating resilient electrical contacts between the rewiring layer, with the semiconductor chip mounted on it, and the printed circuit board. Technically, this can be realized for instance as follows. A chip is positioned by a chip bonder directly from the wafer onto the board and pressed against so strongly that a glue or adhesive layer located between the chip and the board brings about the adhesion of the chips on the board. Because the thickness of the adhesive layer is less than the height of the unstressed elastic interconnect elements, the chip bonder presses the elastic contacts down hard enough during the positioning that the mechanical stop is reached through the adhesive layer. The elastic interconnect elements prestressed in this way form a reliable electrical contact between the chip and the board or the rewiring layer.
The cycle time for producing the connections is very short and can amount to less than one second. If moreover the adhesive force is dimensioned such that the semiconductor chip can be detached from the board again at a defined perpendicular tensile stress, then easy replacement of a defective chip on the board is possible. At the same position, a new semiconductor chip can easily be mounted. If the electrical connection of the pressure contacts does not meet the desired requirements, then by an ensuing thermal process, such as soldering, adhesive bonding, or the creation of intermetallic phases, a further mechanical reinforcement of the connection and/or improvement of the electrical contact properties can be attained. However, this requires preparation of the contact elements prior to mounting.
The adhering intermediate layer for connecting the semiconductor chip and the board can, in a first variant, be embodied as an adhesive film that is adhesive on both sides and that in its thickness is slightly less than height of the unstressed elastic interconnect elements. The adhesive force on the board side is expediently markedly greater than on the chip side, so that the semiconductor chip can be easily removed from the board again if needed, and a new chip can be put in place. The adhesive film can be embodied in multiple parts or perforated, in which case the interconnect elements are disposed in the gaps.
In another variant, a one-piece pierced or multi-part base can additionally be applied to the wafer having the already-applied elastic interconnect elements; for instance, the base can be applied using the cost-saving pressing technique. The base layer is in turn slightly lower than the elastic contacts and thus forms a vertical stop when the board is put in place. The application of a very thin adhesive layer can be done either on the board or on the wafer. If it is applied to the wafer, then in a further function, including test runs and so-called burning-in, it can serve as an adhesive/adhering connection, which makes it unnecessary to use conventional bases with mechanical snap closures.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electronic component with at least one semiconductor chip and a method for producing the electronic component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.